This invention relates to a rotary aerator having a rotor mounted for rotation about a horizontal axis for the introduction of air or other gases into waste water or similar fluids by a plurality of agitator elements formed integrally with hub portions assembled to provide generally star-shaped members which extend radially from the circumference of the rotor along the entire length thereof.
In prior art equipment such as that described in German patent No. 1 135 835 the agitating means has consisted of metal blades having their roots or surfaces lying between blades extending in a circumferential direction and bolted together to form star-shaped members which are rigidly connected to a rotor shaft by retaining means.
Depending upon the liquid in which it operates, the rotor is more or less exposed to the effects of corrosion, in particular if waste water is being treated. Furthermore, the transition between the metal blades and the root portion lying between adjacent blades defines a narrow bending radius which reduces the bending fatigue strength of the rotor.
In accordance with our present invention we eliminate the above-mentioned disadvantages by providing a rotor having agitator elements formed integrally with a hub portion with the integrally formed members being of a corrosion resistant synthetic plastic material whereby the bending fatigue strength of the rotor is not reduced and an increased corrosion resistance is provided. Also, the weight of the rotor unit is decreased whereby the need for heavy supports is reduced and the cost of production is greatly reduced. The agitator elements of the rotor are assembled in groups of several elements molded integrally with a common hub part or segment so as to provide an integral unit formed of synthetic plastic material. Preferably, the hub portions are molded to provide segments of a cylindrical sleeve-like member.
Since the agitator elements and their respective hub parts form integrally molded plastic members, the transition between root portions and adjacent blade and hub parts no longer poses any problems. The agitator elements are molded integrally with their respective segmental hub parts and are disposed in a plane extending transversely of the rotor unit. Due to slippage or the creep behavior of synthetic plastic material it is usually very difficult to transfer major forces from a plastic member to a rotary member. In accordance with our present invention forces are transferred from the hub to the shaft and the slippage problem is solved by positively interconnecting the adjoining agitator elements so as to prevent them from shifting relative to one another. At least a part of the torque is thus directly transmitted from one agitator element to the next.
To achieve this, adjacent vertical faces of the hub parts of adjoining rotor elements are in frictional contact with each other. In another embodiment, the adjacent vertical faces of the hub parts are provided with projections and recesses for positive engagement with each other in a circumferential direction and, if required, also in a radial direction. The projections and recesses may be of various shapes, such as rectangular or round teeth or pins which engage holes.
Preferably, each recess is staggered relative to the projection at the opposite side of the same hub part in a circumferential direction relative to the pitch of the agitator elements, the displacement being a fraction of the angular distance between adjacent agitator elements. Due to this arrangement, only a limited number of agitator elements will simultaneously dip into the water, which results in improved operational conditions for the unit. That is, the mounting and assembly according to our invention permits a transfer of at least a part of the temporary local peak load directly from one agitator element to the adjacent agitator element.
The hub parts may be fitted with their interior surfaces on a shaft, preferably a hollow shaft, so as to be in frictional contact therewith. The shaft supporting the agitator elements may be relieved of at least part of its load due to the direct transfer of forces between the individual agitator elements. If the hub parts have projections and recesses formed thereon, as described above, no other direct axial contact of adjacent agitator elements is required and the projections do not have to fit tightly into their associated recesses. The agitator elements may be spaced a predetermined distance from each other, so that the deformation of the shaft is limited to certain sections. Another important feature of our shaft-type rotor is that the individual agitator elements and their respective hub parts may be easily dismantled and replaced.
According to our invention, the hub parts may be secured to the shaft and/or to one another by any suitable means. However, it is preferable to fasten the hub parts on the shaft by means of clamping straps, so as not to weaken the shaft by welding or providing holes therethrough, particularly where hollow shafts are employed. Furthermore, our design facilitates mounting and replacement of agitator elements.
A further embodiment of our invention completely eliminates the shaft as a supporting means for the agitator elements. In this embodiment the hub parts together with axially extending clamps form a substantially rigid unit, which also increases the corrosion resistance of the unit considerably and further decreases its weight. The hub parts are thus assembled to form a hollow shaft and may be connected by means of axially extending tie rods or the like which are preferably positioned inside the hollow shaft whereby they are protected against corrosion.
The tie rods are connected to transverse end plates. In addition, the tie rods may extend through and be supported in openings provided in bosses of hub parts or provided in additional rings or disks, with the openings being arranged circumferentially in a transverse plane. This arrangement adds to the stability of the unit since the additional rings or disks may be similar in shape and structure to the hub parts and do not carry agitator elements. They may, however, be narrower than the hub parts.
In another embodiment the axially adjoining, vertical faces of the hub parts are formed to receive pressure absorbing members therein which when assembled are in contact with one another. These members relieve the load on the plastic material and the creeping tendency of the plastic material may be overcome by providing interlocking projections and recesses at opposite ends of the pressure absorbing members. The pressure absorbing members preferably extend over the entire axial length of the rotor whereby extremely high forces may be applied.